Solid state transducer dies having reflective features over contacts and associated systems and methods

ABSTRACT

Systems and methods for improved light emitting efficiency of a solid state transducer (SST), for example light emitting diodes (LED), are disclosed. One embodiment of an SST die in accordance with the technology includes a reflective material disposed over electrical connectors on a front side of the die. The reflective material has a higher reflectivity than a base material of the connectors such that light traveling toward the connectors reflects back out of the device.

TECHNICAL FIELD

The present technology generally relates to solid state transducer (SST)dies having patterned contacts. For example, several embodiments of thepresent technology are related to improving the light output of a lightemitting diode (LED) by reflecting light from contacts located on and/orin the light emitting materials.

BACKGROUND

SST dies are used in a wide variety of products and applications relatedto emitting and/or sensing radiation. Several types of SST dies thatemit electromagnetic radiation in the visible light spectrum are used inmobile phones, personal digital assistants (“PDAs”), digital cameras,MP3 players, computers, tablets, and other portable electronic devicesfor backlighting and other purposes. SST dies are also used for signage,indoor lighting, outdoor lighting, vehicle lighting, and other types ofgeneral illumination.

FIG. 1A is a cross-sectional view of a conventional SST die 10 a havinglateral configuration. As shown in FIG. 1A, the SST die 10 a includes anSST 40 on a growth substrate 17. The SST 40 can be an LED having atransduction structure 30 comprising an active material 15 betweenlayers of N-type GaN 16 and P-type GaN 14. The active material 15contains gallium nitride/indium gallium nitride (GaN/InGaN) multiplequantum wells (“MQWs”). The SST 40 also includes a P-type contact 18 onthe P-type GaN 14 and an N-type contact 19 on the N-type GaN 16. Inoperation, electrical power provided to the SST die 10 a via the P-typeand N-type contacts 18 and 19 causes the active material 15 to emitlight.

FIG. 1B is a cross-sectional view of another conventional SST die 10 bin which the P-type and N-type contacts 18 and 19 are in a verticalconfiguration. During formation of the SST die 10 b, the N-type GaNmaterial 16, active material 15 and P-type GaN material 14 are grown ona growth substrate (not shown in FIG. 1B), which can be similar to thegrowth substrate 17. After forming the transduction structure 30, acarrier 20 is attached to the P-type contact 18. For example, one sideof the P-type contact 18 can be attached to the P-type GaN 14 and theother side of the P-type contact 18 can be attached to the carrier 20using a bond material 22, which can be composed of metal or metal alloylayers. The bond material can be a Ni—Sn—Ni stack such that one Ni layercontacts the carrier 20 and the other Ni layer contacts the P-typecontact 18. Other bond materials, such as CuSn and/or TiSi, can be used.Next, the growth substrate can be removed and the N-type contact 19 canbe formed on the N-type GaN 16. The structure is then inverted toproduce the orientation shown in FIG. 1B.

Most electronic devices and many other applications require a whitelight output. However, true white light LEDs are not available becauseLEDs typically emit light at only one particular wavelength. For humaneyes to perceive the color white, a mixture of wavelengths is needed.One conventional technique for emulating white light with LEDs includesdepositing a converter material (e.g., a phosphor) on an LED. Forexample, FIG. 2A shows a conventional lighting device 30 a that includesa device substrate 50, an SST die 10 a or 10 b mounted on the devicesubstrate 50, and a converter material 60 on the SST die 10 a-b. Thelight emitted from the SST 40 undergoes at least partial conversionwhile passing through the converter material 60 as explained in moredetail below with respect to FIG. 2C.

Multiple SST dies 10 a-b can be used in a lighting device. For example,FIG. 2B is a cross-sectional view of a conventional multi-SST lightingdevice 30 b having the device substrate 50, a plurality of SST dies 10a-b attached to the device substrate 50, and the converter material 60over the SST dies 10 a-b. The multi-SST lighting device 30 b also has asingle lens 80 over the SST dies 10 a-b. Other conventional multi-SSTlighting devices may have a dedicated lens per SST or a group of SSTs.All the SSTs 40 in the multi-SST lighting device 30 b are typicallyconnected to a common anode and cathode such that all of the SST dies 10a-b operate together.

FIG. 2C schematically illustrates the light frequency conversion andscattering/reflection in a conventional lighting device 30 c in whichthe lens 80 encloses the SST 40 and the converter material 60. The SST40 emits blue light (B) that can stimulate the converter material 60 toemit light at a different frequency, e.g., yellow light (Y). Some bluelight (B) emitted by the SST 40 passes through the converter materialwithout stimulating the converter material 60. Other blue light (B)emitted by the SST 40 stimulates the converter material 60, which, inturn, emits yellow light (Y). The combination of the emissions of bluelight (B) from the SST 40 and the emissions of yellow light (Y) from theconverter material 60 is designed to appear white to a human eye if theblue and yellow emissions are matched appropriately. However, not alllight emitted by the SST 40 ultimately leaves the lighting device 30 c.For instance, the converter material 60 scatters some blue light (B)back toward the SST 40. Additionally, some light that reaches the outeredge of the single lens 80 reflects back toward the converter material60 and further toward the SST 40.

FIGS. 3A-3C show top views of several conventional lighting devicesconstructed as schematically illustrated in FIGS. 1B and 2A withdifferent patterns of N-type contacts over the N-type GaN of the SSTs40. The patterns of N-contacts are designed to distribute electricalcurrent through the N-type GaN to other relevant parts of the SST. Someexamples of the N-contact patterns are rail-type N-contacts runningwithin the outline of the SST 40 (FIG. 3A), dot-type N-contactsdistributed over the SST 40 (FIG. 3B), and rail-type N-contactsextending beyond the outline of the SST 40 (FIG. 3C). The N-contacts 19can cover an appreciable percentage of the surface area of the SST 40.Since the N-contacts 19 may absorb a significant portion of the lightthat is scattered from the converter material, refracted from the lens80, or reflected from other objects (not shown), the N-contacts 19 arerelatively “dark regions” on the surface of the SST that reduce theoutput. Consequently, even though a particular N-contact layout mayimprove the distribution of electrical current through the SST 40,conventional N-contacts may impair the visual appearance and reduce theefficiency of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale. Instead, emphasis is placed on clearlyillustrating the principles of the present disclosure. Furthermore, inthe drawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1A is a partially schematic, cross-sectional illustration of an SSTdie having lateral contacts in accordance with the prior art.

FIG. 1B is a partially schematic, cross-sectional illustration of an SSTdie having vertical contacts in accordance with the prior art.

FIG. 2A is a partially schematic, cross-sectional illustration of an SSTlighting device having a converter material in accordance with the priorart.

FIG. 2B is a partially schematic cross-sectional illustration of amulti-SST lighting device having a lens in accordance with the priorart.

FIG. 2C is a schematic illustration of light refraction and reflectionfrom the converter material and lens in accordance with the prior art.

FIGS. 3A-3C are top views schematically illustrating N-contact layoutsfor SST devices in accordance with the prior art.

FIG. 4A is a partially schematic, cross-sectional illustration of an SSTdie in accordance with an embodiment of the presently disclosedtechnology.

FIG. 4B is a partially schematic, cross-sectional illustration of apackaged SST device with a lens in accordance with an embodiment of thepresently disclosed technology.

FIGS. 5A and 5B are partially schematic, cross-sectional illustrationsof SST dies in accordance with another embodiment of the presentlydisclosed technology.

FIG. 6 is a partially schematic, cross-sectional illustration of apackaged SST device with a lens in accordance with another embodiment ofthe presently disclosed technology.

DETAILED DESCRIPTION

Specific details of several embodiments of representative SST dies andassociated methods of manufacturing SST dies are described below. Theterm “SST” generally refers to a solid-state transducer that includes asemiconductor material as an active medium to convert electrical energyinto electromagnetic radiation in the visible, ultraviolet, infrared,and/or other spectra. For example, SST dies include solid-state lightemitters (e.g., LED dies, laser diodes, etc.) and/or sources of emissionother than conventional electrical filaments, plasmas, or gases. LEDsinclude semiconductor LEDs, PLEDs (polymer light emitting diodes), OLEDs(organic light emitting diodes), and/or other types of solid statedevices that convert electrical energy into electromagnetic radiation ina desired spectrum. In some embodiments, SST dies can includesolid-state devices that convert electromagnetic radiation intoelectricity. A person skilled in the relevant art will also understandthat the technology may have additional embodiments, and that thetechnology may be practiced without several of the details of theembodiments described below with reference to FIGS. 4A-6.

Briefly described, several embodiments of SST dies and devices havingSST dies disclosed below improve the emitting efficiency compared to theconventional devices described above with reference to FIGS. 1A-3C. Whenenergized, the active material of the SST emits light, but a portion ofthe light refracts or reflects back toward the SST die from either theconverter material or the interface between the lens and air. Theelectrical contacts on the conventional SST dies absorb the returnedlight, which reduces the light output and creates an appearance ofundesirable dark areas on the surface of the SST die. To resolve thisproblem, several embodiments of the present technology have a reflectivematerial over, covering, or otherwise proximate to at least a portion ofselected electrical contacts to reflect the returned light away from theelectrical contacts. For example, depending on the orientation of thedie, the reflective material can be on, above (upward facing dies),below (downward facing dies), and/or around the selected electricalcontacts. This reduces absorption of the light by the contacts andconcomitantly increases the efficiency and enhances the visualappearance of the SST die.

FIG. 4A illustrates an SST die 100 a in accordance with embodiments ofthe presently disclosed technology. The SST die 100 a can have a supportsubstrate 120 and an SST 130 attached to the support substrate 120 usinga bond material 122. The SST 130 can have a transduction structure 131that includes an active material 135 (e.g., gallium nitride/indiumgallium nitride (GaN/InGaN) having multiple quantum wells) between afirst semiconductor material 133 (e.g., P-type GaN) defining a back side132 a of the transduction structure 131 and a second semiconductormaterial 137 (e.g., N-type GaN) defining a front side 132 b of thetransduction structure 131. In general, the front side 132 b faces inthe direction E that light or other radiation passes from and/or to theSST 130, while the back side 132 a faces toward the support substrate120. The SST 130 can further include a first connector 141 (e.g., P-typeconnector) at the back side 132 a of the transduction structure 131 andone or more second connectors 142 (e.g., N-type connectors) the frontside 132 b of the transduction structure 131. The second connectors 142can be, for example, elongated rails or distributed dots disposed overthe front side 132 b of the SST 130. The layout and shape of the secondconnectors 142 is selected to distribute electrical current flow throughthe transduction structure 131. The bond material 122 can be a stack ofNi and Sn materials. Other bond materials are also possible. Theillustrated support substrate 120 has the same width as the SST 130,i.e., the sides of the support substrate 120 are aligned with the sidesof the SST 130, but the support substrate 120 can also be wider anddeeper than the outline of the SST 130.

The second connectors 142 can include a base material 143 on the secondsemiconductor material 137 and a current spreading material 144 on thebase material 143. The second connectors 142 can further include areflective material 146 over (e.g., on, covering, around and/orotherwise proximate to) the base material 143 and the current-spreadingmetal 144. In some embodiments of the SST die 100 a, the secondconnectors 142 do not include the current spreading material 144 suchthat the reflective material 146 directly contacts the base material.The reflective material 146 can be deposited over the base material 143and/or over the current-spreading material 144 using vacuum evaporation,sputtering, or chemical vapor deposition or other suitable processesknown in the art.

The base material 143 and/or the current spreading material 144 of thesecond connectors 142 can have a first reflectivity. The base material143, for example, can be a titanium-aluminum alloy, other alloys ofaluminum, aluminum, and/or other suitable conductive materials. Thecurrent spreading material 144 should have good electrical conductivityand avoid adverse interaction with the base material 143 and thereflective material 146. The current spreading material 144, forexample, can be gold. The reflective material 146 can have a secondreflectivity greater than the first reflectivity of the base material143 and/or the current spreading material 144. The reflective material146, for example, can be silver, a silver alloy, aluminum, polishedmetals, or other materials having high a reflectivity. The firstconnector 141, which can be a P-type connector, should also have a highreflectivity to reflect the emitted and the returned light away from thefirst connector 141. The first connector 141, for example, can also besilver or a silver alloy.

FIG. 4B illustrates a packaged SST device 100 b that includes the SSTdie 100 a, a converter material 160 over the SST die 100 a, and a lens180 over the converter material 160. In operation, a portion of thelight scattered/reflected from the converter material 160 and/or thelens 180 returns toward the SST 130 and impinges either on thereflective material 146 or the active material 130. The reflectivematerial 146 reflects most of the light away from the front side 132 bof the transduction structure 130 such that the additional reflectedlight increases the overall efficiency of the SST die 100 a compared toconventional devices without the reflective material 146. Furthermore,the second connectors 142 do not appear as dark compared to theconnectors in conventional configurations without the reflectivematerial 146.

FIG. 5A illustrates an SST die 200 a in accordance with anotherembodiment of the presently disclosed technology. The SST die 200 a issimilar to the embodiments described in conjunction with FIGS. 4A-4B,but the SST die 200 a has a buried contact. In the illustratedembodiment, the SST die 200 a has an SST 230 with a transductionstructure 231 including an active material 235 between a firstsemiconductor material 233 and a second semiconductor material 237. Thefirst semiconductor material 233 may be a P-type GaN and the secondsemiconductor material 237 may be an N-type GaN, or alternatively thefirst semiconductor material 233 may be an N-type GaN and the secondsemiconductor material 237 may be a P-type GaN.

The SST 230 also has a first connector 241 at a back side 232 a of thetransduction structure 231 and a second connector 242 buried in thetransduction structure 231 under a front side 232 b of the transductionstructure 231. The first connector 241 can be a P-type connectorelectrically coupled to the P-type first semiconductor material 233, andthe second connector 242 can be an N-type connector electrically coupledto the second semiconductor material 237. The second connector 242 caninclude a conductive base material 243 having a first reflectivity and areflective material 246 having a second reflectivity over (e.g., on,covering and/or at least proximate to) at least a portion of the basematerial 243 that faces the front side 232 b of the SST 230. The secondreflectivity of the reflective material 246 is greater than the firstreflectivity of the base material 243.

The SST 230 further includes an insulation material 240 electricallyseparating the base material 243 of the second connector 242 from theactive material 235, the first semiconductor material 233, and the firstconnector 241. Suitable insulation materials include, for example,ceramics, oxides, polymers, epoxies, and other dielectric materials knowto persons skilled in the art. The SST 230, which includes thetransduction structure 231, the first connector 241, the secondconnector 242, and the insulation material 240, can be bonded to asupport substrate 220 by a bond material 222. The support substrate 220and the bond material 222 can be similar to those described in referenceto FIGS. 4A-4B.

In operation, an electrical current flowing through the first and thesecond connectors 241 and 242 causes the transduction structure 231 toemit light. A portion of the emitted light refracts/reflects back towardthe reflective material 246, which in turn reflects this light away fromthe SST 230. The SST 230 with the reflective cover 246 accordinglyimproves the output efficiency and reduces dark areas compared toconfigurations without the reflective material 246.

FIG. 5B illustrates an SST die 200 b in accordance with anotherembodiment of the presently disclosed technology. Here, the reflectivematerial 246 completely covers the portion of the second connector 242in electrical contact with the second semiconductor material 237. Forexample, the side and top surfaces of the upper portion of the secondconnector 242 can be coated by the reflective materials 246. Theincreased coverage of the second connector 242 by the reflectivematerial 246 can further increase the amount of light emitted by thedevice.

FIG. 6 illustrates an SST device 300 having the SST die 200 a of FIG.5A, a converter material 360, and a lens 380. In operation, a portion ofthe light emitted from the active material 235 can scatter from theconverter material 60 or reflect from the edge of the lens 80. Thescattered/reflected light reflects from the reflective material 246, andas described above, the higher reflectivity of the reflective material246 increases the amount of light that is emitted by the SST device 300.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. For example, different materials can be used for SST devicesand/or the substrates in further embodiments. Furthermore, thestructures of the devices may differ from those shown in the Figures.For example, several SST dies can be combined into one SST device and/orone package. The reflective material can be used to at least partiallycover the substrate carrier to further increase overall amount of thelight reflected outside of the SST die. In at least some embodiments,the insulation material facing toward outside of the SST die can bepartially covered with the reflective material, while preserving thefunction of the insulation material. Moreover, while various advantagesand features associated with certain embodiments have been describedabove in the context of those embodiments, other embodiments may alsoexhibit such advantages and/or features, and not all embodiments neednecessarily exhibit such advantages and/or features to fall within thescope of the technology. Accordingly, the disclosure can encompass otherembodiments not expressly shown or described herein.

1. A light emitting diode (LED), comprising: a transduction structureincluding a back side, a front side opposite the back side, a firstsemiconductor material having a first surface at the back side, a secondsemiconductor material having a second surface at the front side, and anactive material between the first and second semiconductor materials; afirst electrical connector electrically coupled to the firstsemiconductor material; and a second electrical connector having a basematerial electrically coupled to the second surface of the secondsemiconductor material, and a reflective material over the basematerial, wherein the reflective material has a higher reflectivity thanthe base material, and wherein the second surface of the secondsemiconductor material is only partially covered by the reflectivematerial.
 2. The LED of claim 1 wherein the second electrical connectorfurther comprises a current spreading material between the base materialand the reflective material.
 3. The LED of claim 2 wherein the basematerial is at least one of a Ti—Al alloy and Al, the current spreadingmaterial is Au, and the reflective material is at least one of Al, Ag oran Ag alloy.
 4. The LED of claim 1 wherein the second electricalconnector comprises a plurality of traces of the base material on asurface of the second semiconductor material, and wherein the traces areat least partially covered by the reflective material.
 5. The LED ofclaim 1 wherein the second electrical connector comprises a buriedcontact having the base material extending through the firstsemiconductor material and the active material from the back side of thetransduction structure to a depth in the second semiconductor material,the reflective material covering at least a portion of the base materialwithin the second semiconductor material, and an insulation materialelectrically isolating the second electrical connector from the firstsemiconductor material and the active material.
 6. The LED of claim 5wherein the base material is at least one of a Ti—Al alloy and Al, andthe reflective material is at least one of Al, Ag or an Ag alloy.
 7. TheLED of claim 5 wherein the base material comprises: a top side facingthe first side of the transduction structure, and a lateral side facingthe insulation material, wherein the reflective material covers at leastthe top side and a portion of the lateral side of the base material. 8.The LED of claim 1, further comprising a converter material disposed atleast partially around the active semiconductor material.
 9. A lightemitting diode (LED) device, comprising: a support substrate; an LED dieon the support substrate, the LED die including a back side facing thesupport substrate, a front side opposite the back side, a firstsemiconductor material having a first surface at the back side, a secondsemiconductor material having a second surface at the front side, and anactive material between the first and second semiconductor materials; afirst electrical connector electrically coupled to the firstsemiconductor material; a second electrical connector having a trace ofa base material on the second surface of the second semiconductormaterial and a reflective material over the base material, wherein thereflective material has a higher reflectivity than the base material,wherein the reflective material is in a path of a light leaving the LED,and wherein the light impinging on the reflective material is mostlyreflected away from the LED; a converter material at least partiallyaround the semiconductor die; and a lens over the LED die.
 10. A lightemitting diode (LED) device, comprising: a support substrate; an LED dieon the support substrate, the LED die including a back side facing thesupport substrate, a front side opposite the back side, a firstsemiconductor material having a first surface at the back side, a secondsemiconductor material having a second surface at the front side, and anactive material between the first and second semiconductor materials; afirst electrical connector electrically coupled to the firstsemiconductor material; a second electrical connector comprising aburied contact having a base material extending through the firstsemiconductor material and the active material to a depth in the secondsemiconductor material, and a reflective material covering at least aportion of the base material within the second semiconductor material,wherein the reflective material has a higher reflectivity than the basematerial; an insulation material electrically isolating the secondelectrical connector from the first semiconductor material and theactive material; a converter material disposed at least partially aroundthe active semiconductor material; and a lens forming a cavity forhousing at least the LED die.
 11. A method of manufacturing lightemitting diode (LED) dies, comprising: forming a transduction structurehaving a back side, a front side opposite the back side, a firstsemiconductor material having a first surface at the back side, a secondsemiconductor material having a second surface at the front side, and anactive material between the first and second semiconductor materials;forming a first electrical connector electrically coupled to the firstsemiconductor material; and forming a second electrical connectorelectrically coupled to the second semiconductor material byelectrically coupling a base material of the second electrical connectorto the second semiconductor material, and depositing a reflectivematerial over the base material, wherein the reflective material has ahigher reflectivity than the base material, and wherein the secondsurface of the second semiconductor material is only partially coveredby the reflective material.
 12. The method of claim 11, furthercomprising forming a current spreading material on the base materialbefore depositing the reflective material such that the currentspreading material is between the base material and the reflectivematerial.
 13. The method of claim 12 wherein the base material is atleast one of a Ti—Al alloy and Al, the current spreading material is Au,and the reflective material is at least one of Al, Ag or an Ag alloy.14. The method of claim 11 wherein forming the second electricalconnector comprises disposing a plurality of traces of the base materialon a surface of the second semiconductor material, and whereindepositing the reflective material comprises at least partially coveringthe base material.
 15. The method of claim 11, further comprisingdisposing an insulation material electrically between the secondelectrical connector and each of the first semiconductor material andthe active material.
 16. The method of claim 15 wherein forming thesecond electrical connector comprises constructing a buried contacthaving the base material extending through the first semiconductormaterial and the active material from the back side of the transductionstructure to a depth in the second semiconductor material.
 17. Themethod of claim 16 wherein the base material is at least one of a Ti—Alalloy and Al, and the reflective material is at least one of Al, Ag oran Ag alloy.
 18. The method of claim 11, further comprising providing aconverter material at least partially around the active semiconductormaterial.
 19. The method of claim 11, further comprising providing alens at least partially around the active semiconductor material.
 20. Amethod of manufacturing a light emitting diode (LED) device, comprising:forming a transduction structure having a back side, a front sideopposite the back side, a first semiconductor material at the back side,a second semiconductor material at the front side, and an activematerial between the first and second semiconductor materials; disposinga first electrical connector electrically coupled to the firstsemiconductor material; disposing a second electrical connectorelectrically coupled to the second semiconductor material byelectrically coupling a base material of the second electrical connectorto the second semiconductor material, and disposing a reflectivematerial over the base material, wherein the reflective material has ahigher reflectivity than the base material, wherein the reflectivematerial is in a path of a light leaving the LED, and wherein the lightimpinging on the reflective material is mostly reflected away from theLED; providing a converter material at least partially around the activesemiconductor material; and providing a lens at least partially aroundthe active semiconductor material.
 21. The method of claim 20, furthercomprising disposing a current spreading material between the basematerial and the reflective material.
 22. The method of claim 21 whereinthe base material is at least one of a Ti—Al alloy and Al, the currentspreading material is Au, and the reflective material is at least one ofAl, Ag or an Ag alloy.